The problem is mainly the change in graphics and general art design. In d1, there was a focus on smaller details and lighting. I also think that the general silhouettes of the guardians were more human and realistic, if that makes any sense. With d2, while the graphics are dazzling at a glance, and the backgrounds are fantastical and seem freshly war-ravaged... there is a sort of cartoony vibe that everything gives off, from the guardians to the enemies. D2 is dark thematically, but visually it is not quite as believable imo, with its intense color saturation and exaggerated class differences in stance and silhouette. Couple this with the less serious dialogue and the general light-hearted take on the enemies which are often seen almost as more of an annoyance than a threat, despite the obvious dangers that each enemy faction poses, and you’ve got a game where things are more “entertaining” than believable, threatening, or foreboding. TLDR: in my opinion, d1 has a more realistic and believable art design, with subtle details making all the difference. D2 has a cartoony feel for reasons which can be summed up with the word “exaggeration”.